NAME:
  fluxref
 PURPOSE:   (one line only)
  Provide standard fluxes for standard filters
 DESCRIPTION:
 CATEGORY:
  Astronomy
 CALLING SEQUENCE:
  fluxref,filter,wave,flux,sun
 INPUTS:
  filter - String, name of a filter to look up
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  REFFILE - Name of file to load.  Default is support_files/luxref.dat that
             must exist in your IDL_PATH.  This will be satisfied by this
             library for the default.  The first one found will be loaded.  If
             you want to load an explicit file not in your path you need
             to provide a full qualified path (starts with /) and the path
             search is avoided.
  RELOAD - Flag, if set forces a re-read of the flux file.
 OUTPUTS:
  wave - pivot wavelength (microns)
  flux - absolute flux for the filter, in ergs/cm^2/s/A (Vega mag system)
  sun  - absolute flux for the sun through the filter, same units as flux
 KEYWORD OUTPUT PARAMETERS:
 CONFIGURATION:
 COMMON BLOCKS:
  fluxref_com - used to cache the data from the reference file, not intended
                  to be used by any other routines.
 SIDE EFFECTS:
  If there are useful standard values not present in the file that you
    would like, send a request to have it added.
 RESTRICTIONS:
 PROCEDURE:
  There is a file, fluxref.dat, that lives with the library.  On the first
    call to this routine, this file is read and saved in a local common
    block to cache the data.  All subsequent calls will use the data in 
    memory.  The /RELOAD flag is provided to force it to re-read the file
    but this flag is not intended for programmatic use since this situation
    is likely to come up only during development.
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2021/08/24 and based
    on prototype code written by Brian Keeney.
  2021/09/02 - MWB, added sun flux on output